Apparatus for kiln drying



July 20, 1937. J. l. STEEL ,0

APPARATUS FOR KIL N DRYING Filed Feb. 25, 1952 4 Sheets-Sheet l *Q if 8 ll mm HT 11 M: W 8, Q a M i fi a a i L m p m QM H m mm 4 an H July 20, 1937. J STEEL 2,087,454

APPARATUS FOR KILN DRYING Filed Feb. 25, 1932 4 Sheets-Sheet 2 n 3 M o k/a lgl:

igl L F/gllf F/gZZT y 1937. J. 1. STEEL 2,087,454

APPARATUS FOR KILN DRYING Filed Feb. 25, 1932 4 Sheets-Sheet 5 Illl/ I 31 llll I n l I A II I ll 4 INV NT July 20, 1937. J. l. STEEL APPARATUS FOR KILN DRYING Filed Feb. 25, 1.932 '4 Sheets-Sheet 4 Patented July 20, 1937 UNITED STATES PATENT OFFICE APPARATUS FOR KILN DRYING Application February 25, 1932, Serial, No. 595,052

8 Claims.

My invention relates to improvements in the art of drying stocks such as lumber products, and particularly to the method of, and apparatus for drying of materials, varying in initial moisture content, such for example, as mixed heart and sapwood of green hardwoods or softwoods, in order to bring them to a more uniform moisture content, in a preliminary drying chamber prior to their being subjected to a kiln drying process and later to a reconditioning process.

An object of my invention is to provide an economical drying system for preliminary drying of lumber products for example, preferably with controlled temperature and with humidity lower than the average atmospheric humidity, to reduce the stock to a substantially uniform predetermined moisture content.

Another object of my invention is to supplement the regular kiln drying process, with an economical preliminary drying process, permitting the use of one handling of the stock, instead of two as commonly used when stock is stacked in the open, in the yard, preliminary to kiln drying, and thus to reduce the investment usually required in air drying yards, and in regular dry kilns.

Another object of my invention is to employ a preliminary drying chamber, in which I exhaust the coolest atmosphere, namely the strata along the floor, and thus prevent moulding of the stock and promote the equalization of moisture content of the stock.

Another object of my invention is to provide a large capacity multiple track preliminary dryer that will be economical to construct and to operate, preparatory to drying in regular single track dry kilns, and which will give more satisfactory preliminary drying results than yard drying, in a much shorter period of time, and in a more economical manner.

Another object of my invention-is to provide a preliminary drying chamber which will rapidly remove the free water from substances such as lumber, preferably at low temperatures, and thereby to produce drying that will preserve the quality of the product.

Another object of my invention is to maintain a suitable preliminary drying atmosphere for stock in accumulated storage in a multiple track preliminary drying chamber preparatory to its being charged into regular kilns, and to maintain mechanical circulation of said suitable drying atmosphere across the stock.

Another object of my invention is to efiect greater economy in power consumption in the preliminary drying chamber by employing heat: ed atmosphere supplied from a suitable outside source, such as heat from an adjacent kiln or, direct or indirect heat such as from a gas or oil fired burner.

Another object of my invention is to provide a novel ventilating system for a dry kiln. This system preferably is employed when vented atmosphere may be employed elsewhere, for its heat or moisture content.

Another object of my invention is to provide means of rapidly equalizing the initial moisture content of stock thru preliminary drying of both low and high moisture content boards for example, which latter more. rapidly lose moisture 5 under preliminary drying conditions, thus making possible greater efiiciency in the regular kiln drying process.

Another object of my invention is to effect better bafiiing of the stock loads by a novel baffling means.

Another object of my invention is to reduce the need for sorting lumber according to moisture content before kiln drying, by a preliminary equalizing treatment which tends to bring all the boards, for example, in a stock load of stock, varying in initial moisture content, to a more uniform moisture content before being dried to a desired average moisture content in the regular dry kiln.

Another object of my invention is to produce a novel preliminary drying chamber which will adequately protect the unseasoned lumber in storage from sunshine, rain, and the adverse drying conditions. This is designed to replace the more expensive and less efiective method of preliminary air drying lumber, by stacking it in the open atmosphere in the yard before stacking it for the regular kiln drying process.

Another object of my invention is to provide a novel process of drying which consists in producing a more equalized initial moisture content of one board with another in a stock load, in a preliminary drying chamber, and then drying them to an average moisture content in a separate kiln, later equalizing the moisture content within each board in a reconditioning chamber, thus giving better drying results than have heretofore been possible.

It is recognized that progressive type kilns are old in the art. Such kilns maintain a high humidity and lower temperature at the green end of the kiln into which lumber is put at periodic intervals. As the stock is made to progress through such kilns from one stage to another, the humidity is reduced and the temperature gradually raised. The preliminary drying chamber of my present invention is an extra step in the drying process, in addition, and

gressive or charge type kiln. My preliminary dryer is new in the art and is described in detail in the following specification.

What constitutes my invention will be herein- 10 after specified in detail and succinctly defined in the appended claims.

Figure I is a plan view of my preliminary dryling chamber showing the arrangement of the stock supporting tracks and an air circulation 15 system.

Figure II is a partial plan view of an alternate arrangement of fan circulating system. to that shown in Figure I.

Figure III is a transverse vertical section taken along the lines III--III of Figures I and V.

Figure IV is a transverse vertical section, show-- ing a modified circulating system from that shown in Figure III with provision for recirculation.

Figure V is a longitudinal vertical section taken along. the lines V-V of Figures I and III.

Figure VI is a transverse section of a modified recirculating system from that shown in Figure IV, with fans located below the partition floor, and the lumber in the stock loads stacked on edge. The fan duct system in Figure VI is illustrated in plan in Figure VII.

Figure VII is a diagrammatic plan view of a kiln layout illustrating the preliminary drying 35 chamber, the regular kilns, and a reconditioning chamber or cooling shed. The fan system in the preliminary drying chamber being a modified form of that illustrated in FigureI. Figure VII shows a diagrammatic illustration of temperature and humiditycontrol instruments.

Figure VIII is a side elevation of the layout taken along the lines VIIIVIII of Figure VII.

Referring to the numerals on the drawingsl indicates the floor of a preliminary drying chamber which may be a platform of usual dock construction, preferably in front of a battery of dry kilns. 3 and 4 are the side walls, and 5 the roof, of any preferred form of enclosed structure, which may house stock loads of lumber 6 which may be stored for preliminary drying, preparatory to kiln drying in the regular type of kilns 2. Suitable doors 8 and 9 are provided at each end of the preliminary drying chamber l0. These doors may be of any suitable construction, such as canvas, roller sliding doors, or any other t pe which may be suitable for closing the ends of the preliminary drying chamber I0. In some cases doors may be employed at one end only of the preliminary drying chamber, in which case the opposite end would be closed. The regular ploy a common door for the preliminary drying chamber ill and the regular kilns 2.

The interior of the chamber is designated I and I I, ll being a recirculation space, which may 'be used if desired, and may be located above or below the stock loads which are in the preliminary drying chamber proper, or, both above and below as illustrated in Figure VI.

The stock loads are preferably supported by bunks l2 which are carried on trucks i3, having wheels which roll on the rails [4, which are supported on the floor I.

The stock loads are preferably stacked with prior to the initial stage of the ordinary prokilns 2 have doors also, and in some cases I emspacing stickers l6 between layers providing ining pipes 20 in the space I 5 between the stockloads and, the pipes 2| adjacent to the side walls 3 and '4 of the chamber. The pipes 20 may be placed within the space between and adjacent to the stock loads, or they may be placed in alternate spaces between the tracks as illustrated in Figure III. The function of the pipes 20 is to heat the atmosphere after it passes through one or more stock loads, in order to maintain a desired temperature of entering air prior to its passing across other stock loads. In some cases, when the outside air is a suitable drying medium, as, for example, during the summer months, I prefer not to use heating pipes, or, in some cases to omit them from the chamber altogether, and to suck into the preliminary drying chamber suitable outside atmosphere and circulate it through the stock loads.

I prefer to distribute the heating pipes 20 and 2| throughout the length of the preliminary drying chamber in any preferable manner. They may be equally distributed to give the same heating surface throughout the length of the chamber, as shown in Figure I, or more heating surface may be installed at one end than at the other end of the chamber, if desired, to promote faster drying at one end than at theother end.

I preferably provide a reversible circulating 3 or 4, of the preliminary drying chamber III, as

shown in Figures I, III or IV. The circulating system comprises a series of rotary fans 25 and 26 mounted at intervals, preferably on a common shaft 21 extending substantially the full length of the chamber, supported by bearings 23 carried on bearing stands 23, the shaft being rotated by a suitable electric motor 30. Any suitable circulating system, however, may be employed.

The fans 25 are preferably right hand and the fans 26 are preferably left hand, but the combination of right and left hand fans is preferential only, it being understood that all right hand or all left hand fans, or a combination of both may be used toeffect adequate circulation within the chamber. The fans may be opposed in pairs as shown in Figures II and VII, or they. may be arranged to discharge toward the center or opposite ends of the chamber as shown in Figure I. The fans are preferably mounted in suitable openings in cross walls or housings 32 adjoining a partition 3i separating suction compartments 33 from air delivery compartments 34. The side walls of compartments 33 and 34 are defined by the partition 3|, and in some cases by cross partitions 36. Top fan duct plates 23 and bottom plates 24 also form apart of the fan duct system, forming sides of the compartments 33 and 34 aforesaid. The top plates 23 also in some cases form a part of the partition, which separates suction from air delivery compartments. In some cases I also provide bailies 31 and 38 for directing the circulating medium towards the center or the ends of the drying chamber, or toward the bottom or topof the stock loads, as

may be required to effect uniform distribution of circulation and uniform drying within the preliminary drying chamber.

In Figure II the compartments 34 are formed on one side by a partition wall 3|, and the fans in housings 32 which adjoin side walls of the dryer H8, a bottom plate 24 and a top plate 23. Compartments 33 are open on one side into the drying chamber and are also bounded by side wall I I8, cross walls 32 having openings in which fans are mounted, top plates 23 and bottom plates 24. The side wall H8 has dampered openings 60 and 80 opening in the compartments 33 and 34 respectively. These openings act as fresh air and ventilating ports respectively, depending upon the direction of air circulation.

The baflles 31 and 38 are preferably adjustable by flection for distributing the circulating medium. The duct system and baffles 31 and 38 shown in Figure I, may be used in place of the opposed fans shown in Figure II, for exhaust, if desired. For example, Figure IV is shown to have the same duct system as in Figure I with baffles 31 and 38. L

Considering that the fan system is reversible, it will be understood that the suction compartment 33 and the air delivery compartment 34 are relative terms and that the suction compartment will become the air delivery compartment and the air delivery compartment will become the suo-' tion compartment upon reversal of the direction of rotation of the fans. Ports are preferably provided in the compartments 33 and 34 and act as inlet ports 60 or 80, depending upon the direction of fan rotation. Outlet ports may be provided in the roof, as commonly used in kilns, if desired.

I preferably provide closure baflle plates 39 and 48, which direct the air circulation through the stock loads. The closure bafile plates 39 and 40 are preferably located adjacent to the upper corner of the stock load above the heating pipes. The space l between loads is preferably wide enough to accommodate the heating pipes 20, and moisture sprays 56 which may be placed in any desired position within the chamber. The closure baffle plate between a load andthe dryer building, or between loads, may be of any desired form. However, I prefer that they may be of the raising and lowering type 42, hinged and operated by having a series of pulleys 43, spaced along the chamber building, and a flexible line 44 passing therethrough as illustrated in Figure III, or they may be of the fixed type 39 and 48, spaced away from the corner of the loads as indicated in Figure IV. The closure bafile plates 39 and 40 are between loads and are supported in any suitable manner as from the roof supporting posts 4| of the preliminary drying chamber. These closure bafile plates of the adjustable or of the fixed type, function to prevent substantial air leakage vertically between the adjacent corner of the stock load and the dryer building.

When desired the closure plates 42 may be elevated to a position above the top of the stock load until the load is rolled into the chamber on the track rails l4. When the load 6 is on the track, the bafiie 42 may be lowered to contact the top or side of the stock load by releasing the line 44 from the bracket 45 to which it may be fastened. This adjustable baflle plate arrangement may be employed adjacent to one corner of each of the stock loads on each of thetracks on the preliminary drying chamber.

In some cases it is desirable not to recirculate the air within the preliminary drying chamber, but rather to suck in fresh air and to exhaust it after it has \passed across the stock loads. This is illustrated in Figure III in which I preferably provide a fresh air intake 49, an adjustable door 49A, and a ventilating port 50. This system may be also reversed, by reversing the direction of rotation of the fans 25 and 26 and in case this is done the air will be ventilated after passing across the stock loads. For instance, air may be sucked across the stock loads as illustrated in Figure III from right to left, or air may be blown across the stock loads as illustrated in Figure III from left to right. In case the air were sucked across the stock loads by the fan system, the pipes may be used when desired, for example, by supplying them with steam through supply pipes 52, from a source not illustrated. When the air is blown across the stock loads all the pipes may be used with the possible exception of pipes 2| which would be on the air outlet side of the dryer for this direction of circulation. I prefer to circulate the atmosphere in the chamber substantially at right angles to the direction of movement of the stock.

In Figure IV I illustrate a recirculating preliminary drying chamber in which the atmosphere is recirculated across a series of stock loads, in either right to left, or left to right directions. In this design a desired amount of outside air is taken in through the ports 60 through the wall H8 into the suction compartment 33 of the fan system, and part of the circulating atmosphere may be exhausted from the air delivery compartments 34 through the port 80 through the wall H8, shown in Figure II, or recirculated in the chamber through the port 8| shown in Figure VI. Upon reversal of circulation fresh air may be intaken through the port 80 into the compartment 34 and exhausted from the port 68, or recirculated through the port 6|. The port 60 may be equipped with a damper 48 if desired, similar to the damper 85 in the port 80. The specific duct system illustrated in Figure IV is claimed in my application Serial No. 598,006.

I preferably provide also floor deflector plates 5| which prevent air circulation from evading the stock loads as illustrated in Figures III and IV.

I preferably provide automatic temperature and humidity controls or thermostats for the preliminary drying chamber l5, the kilns 2, and the cooling shed 63. These are of any well-known type and I have indicated them for the three above mentioned drying rooms, as 96, 91 and 98 respectively, which are preferably actuated by auxiliary air pressure.

Each of the thermostats 98, 91 and 98 has a dry and a wet bulb, each of which actuates a diaphragm valve, and in some cases a diaphragm motor lever, the dry bulb actuating a diaphragm valve controlling the steam supply to the respective heating pipes, and the wet bulb actuating a diaphragm valve controlling the steam supply to the respective humidifying spray pipes, and in some cases one or more diaphragm motor levers instruments to the respective diaphragm valves or motor levers.

For example, the preliminary drying chamber, an illustrated in Figure I, has ,a thermostat 96, having a dry bulb 65 controlling the dry bulb temperature and actuating a diaphragm valve 41 on the supply to the heating pipes 20, and a wet bulb 68 controlling the wet bulb temperature and actuating the diaphragm valve 46 controlling the humidifying spray pipe 56.

Each of the regular kilns 2 preferably has a thermostat 91, having a dry bulb 66 controlling the dry bulb temperature and actuating the diaphragm valve 99 which controls the supply to the heating pipes I04 in the kiln and a wet bulb 69 controlling the wet bulb temperature and actuating the diaphragm valve I which controls the wet bulb temperature by regulating the discharge from the humidifying spray pipes I05 within the kiln. The wet bulbs 68, 69 and I0 have on them wicks III, which are wet by a supply, not illustrated, of water in the water box 2.

The thermostat 98 controls the dry bulb and wet bulb temperatures in the cooling shed, or reconditioning chamber 63. It has a dry bulb 61 which controls the dry bulb temperature in the cooling shed and actuates a diaphragm valve I M controlling the supply of heat to the heating pipes I 9. t also has, a wet bulb I0 controlling the wet bulb temperature and actuating a diaphragm valve I02 controlling the supply of humidity discharged from the spray pipes. I06 in the cooling shed 63.

The thermostats and the diaphragm valves are preferably of the direct'acting type, the former supplying air to open the latter automatically when the temperature drops below the set point, the source of the air and piping II2 connections of which are not illustrated. The thermostats are of any well known type and are preferably recorder controllers. The bulbs are located in the respective chambers as shown in Figure VII, at any suitable place where they may respond to changes in temperature of the dryingrmedium, and the diaphragm valves are located on the supply pipes to the heating pipes and humidifying pipes respectively at any suitable place.

I also preferably provide any suitable system of humidification in the preliminary drying chamber, such as for example, the sprays 56, preferably located adjacent to each of the heating pipe units 20 and 2| and which permit the discharge of steam or moisture into the circulating atmosphere in the chamber automatically by means of the controlled valve 46, which is actuated by the thermostat having a bulb 68, when the relative humidity is lower than the desired amount, preferably before it passes across the stock loads. In most instances the relative humidity of the atmosphere after passing across a stock load, will be higher than the desired amount, and no additional moisture from the steam sprays will be needed. The relative humidity is reduced by the atmosphere passing across the heating pipes 20. As atmosphere passes across the stock loads 6, it receives moisture from the stock being dried. The stock loads thus act as humidifiers of the atmosphere. For example, sap stock on one track in the preliminary drying chamber would supply the circulating atmosphere with the humidity needed for the protection of heart stock on another track. The heating pipes 20 reheat thelatmosphere between loads passing across them. If the wet bulb temperature is low ad- 'and humidity thermostat 96.

jacent to the thermostat bulb in the kiln, the automatic controls or thermostat will turn on the steam spray. If the wet 'bulb temperature and the relativehumidity become too high, the set point of the wet bulb temperature in an automatic control may be lowered and thus reduce the relative humidity tothe desired point.

When the relative humidity of the atmosphere in the kiln is too high, after passing across the stock loads in the preliminary drying chamber, to permit the atmosphere to be used for further drying, it may be discharged from the chamber, after passing across the chamber once. If the humidity is not too high, all or a part of the atmosphere may be recirculated.

The temperature and humidity control instrument or thermostat 96 may automatically control the amount of air ventilated from the preliminary drying chamber I0 and thus the amount of air recirculated therein. This may be accomplished by controlling the dampers 85, and 48, in the ports 80 and 60 respectively. For this purpose I preferably provide a diaphragm motor lever 84 which is actuated by air pressure released by the automatic control instrument 96 which in turn is actuated by the wet bulb 68.

The motor diaphragm 84 operated by auxiliary air pressure from a source not illustrated, actuates the damper 85, when the temperature in the kiln at the position of the thermostat bulb 68 drops below the set point of the temperature The thermostat admits air through pipes III to the diaphragm motor lever 84, which closes the outlet port 80 and the inlet port 60 as shown in Figures VI and VII. The operation is made slow by the controlled leak I I0, which causes pressure to build up in the diaphragm of the motor lever, 84, very slowly.

If the temperature at the location of the thermostatic bulb 68 rises to the set point, the instrument automatically cuts off the air supply to the diaphragm motor 84, permitting the motor lever spring I 01 to open the ports 80 and 60 by movement of the damper 85 and 48 respectively, which are fixed to the .damper shaft II8 which extends substantially the full length of the kiln. The air pressure which is built up in the motor diaphragm 84 is released through the controlled leak IIO.

The thermostat bulb 68 also may actuate the diaphragm valve I08 controlling the humiditying spray 56 in the chamber simultaneously with the actuation of the motor diaphragm 84. The diaphragm valve I08 is also the direct acting type which opens with air pressure. Simultaneously with the closing of the outlet port 80 and the inlet port 60, the diaphragm valve I08 opens to admit steam to the humidifying sprays. Similarly, the humidifying spray is cut off by release of air pressure on the diaphragm of the valve I08, permitting it to close by means of the spring I09, when the outlet port 80 and the inlet port 60 are opened.-

In Figure VI I illustrate a preliminary drying chamber having stock loads of lumber end piled, stacked on edge. Two fan systems are used, one being on each side of the preliminary drying chamber I0. Recirculation of the atmosphere is provided in the space I I below the stock loads. The partition floor 73 directly beneath the stock loads has a grid opening beneath each load.. The grid openings are preferably of varying sizes. The openings 15 adjacent to the fan are smaller than the openings 11 remote from the fans, while the openings 16 are of intermediate size. The size of these openings is varied to provide substantially equal circulation across the stock loads on the several tracks. If the openings were of the same size, the loads adjacent to the fan system would have the most air circulation across them. In Figure VI, one humidifying system serves each half of the chamber. The heating pipes 20, between loads heat the atmosphere by radiation, while the larger pipe areas 2|, controlled by the thermostat 96 and the diaphragm valves 35, are in the main air flow to or from the fan system and serve the part of the chamber served by the fan system.

Each of the regular kilns 2 preferably has fresh air and ventilating ducts 89 and 92, each of which may serve as fresh air intakes or exhaust ducts depending upon the direction of fan rotation in the kilns 2. Each of these ducts may have doors at each end which may be opened or closed at will, or automatically by any suitable means, such as a diaphragm'motor lever, if desired. The ducts 89 and 92 have ports 95 and 94 respectively for kiln atmospheric communication between the ducts and the kiln. A port in each duct is preferably located near each fan of the kiln 2, the ports 94 being on the suction side of the fan ducts and the ports 95 being on the pressure side of the partition in which the fans are mounted, or vice versa, depending upon the direction of fan rotation. The ducts 89 and 92, as illustrated, employ two side walls of the kiln for two of their sides.

In some cases I prefer to employ heated atmosphere exhausted from one or more of the regular kilns 2, as a circulating medium in the preliminary drying chamber. When this is done, the door 88 of the ventilating duct 89, is open and the door 90 is closed. The door 9| in the air intake duct 92 is closed also and the door 93 is open. In this case air would be intaken into the kiln 2 through the door 93 into the intake duct 92 where it is distributed through the ports 94 into the kiln 2, and by means of internal fans, is delivered to the opposite side of the kiln where it is forced by pressure through the ports 95 into the ventilating duct 89 and out of the door 88 into the recirculating space I I of the preliminary drying chamber, where it is sucked into the suction compartments 33, where it may be recirculated through the ports 8 I, for example, in the preliminary drying chamber I0.

The above ducts 89 and 92 may function respectively as fresh air intake ducts, or ventilating ducts. Each of the ducts has a door at either end, one end opening into the operating pit 95 of the kilns 2, and the other door opening into the recirculation space H of the preliminary drying chamber in. When the circulation in the kilns 2 is reversed, the ventilating duct 89 becomes the air intake duct and the air intake duct 92 becomes the ventilating duct. Thus the door 88 on the air duct 89 is closed, and the door 90 is opened. The air door 93 of the air duct 92 opening in the operating pit, is closed, and the door 9| is opened. In this manner it may be understood that with either direction of circulation air may be intaken from 8 the reconditioning chamber 63, through the air pit 1 and the open grid 22, into the operating pit 95 and into the kilns 2, and vented atmosphere from the kiln 2 may be discharged through the air ventilating ducts 89 or 92 whichever may be on the discharge side of the'fans, into the preliminary drying chamber l0 by opening the door of one of said ducts into the preliminary drying chamber. This air discharged from the kilns 2 into the preliminary drying chamber may be recirculated across the stock loads in said chamber and exhausted when desired or when necessary to maintain the predetermined schedule in the preliminary drying chamber. By employing this system I efiect economy in the regular kiln drying operation by employing waste heat from the kilns, in the preliminary drying chamber.

When desiredfresh air may be intaken into the kilns 2 from the preliminary drying chamber l0, instead of from the operating pit 95, especially during. the reconditioning process, when stock is reconditioned in the kilns 2, or, in some cases, I may employ exhaust atmosphere or waste heat from the kilns 2 in the reconditioning shed 63 in a similar manner to that described above for the preliminary drying chamber. In this case fresh air would be intaken into one of the kilns 2 from the preliminary drying chamber and exhaust vapors would be discharged through the operating pit 95 into the reconditioning shed 63, through the air pit 'l, and the open grid 22.

In this manner the preliminary drying chamber l0, each of the kilns 2 and the reconditioning shed 53 may be interdependent insofar as either one may use waste atmosphere or heat from the adjacent room. This se of heated or humidified atmosphere from one chamber in another may be controlled by manual or any suitable automatic control means.

When lumber at the average plant is stacked on kiln trucks ready for kiln drying, the individual boards vary in moisture content, some of them being sap, have a greater percentage of free water, and having a moisture content above based on oven dry weight, some of them being heart stock having less free water than the sap, having a moisture content below 50%, and some having both heart and sapwood in them. By preliminary drying the moisture content of heart and sap boards of stock loads on the same or different tracks can be substantially equalized at approximately 20% moisture content, for example, by subjecting them both to a preliminary drying atmosphere of F., and 90% relative humidity. In practice I preferably use a lower humidity as complete equalization of initial moisture content requires a longer period of time. The process promotes equalization and this is carried on as long as practicable. After this equalization of moisture content heart and sap stock can be dried together in the ordinary kiln drying process in a single track kiln, and moisture in the cell walls, (hygroscopic moisture) can .be dried out in a minimum of time and very uniformly. When mixed moisture con tent stock is put into the regular dry kiln together without preliminary drying, it is necessary for the drying process to be carried on to meet the needs of the highest moisture content stock. Equalizing themoisture content of the stock in a preliminary drying chamber therefore makes it possible to increase the efficiency of the kiln drying operation and to increase the capacity of regular kilns 2 by use of higher temperatures and lower humidities than would be practicable withv ably maintain a controlled low temperature, in some cases preferably below 110, which is suitable for the preliminary drying of wood having a low critical temperature, and also a controlled humidity. In special preliminary drying treatments any desired temperature and humidity may be maintained. I preferably install heating pipes for raising the temperature slightly above the atmospheric temperature condition, for example, between 70 and 140, and reducing the relative humidity lower than the average outside atmospheric relative humidity condition. In this manner I promote the preliminary drying of the free water from the stock and the equalization of the moisture content of the various boards without substantial degrade. Moisture content determinations are made at intervals to determine the progress in equalization in moisture content and'preliminary drying may be interrupted at any time.

In many cases preliminary drying has been accomplished on the yardthat is, stock, after it is sawn, is moved out into the yard and there stacked in the open in piles, where it is permitted to air dry for a period of 4 to 6 months before it approaches moisture content equilibrium with the prevailing outside atmospheric conditions of that location-usually approximating 15 to 17% moisture content. In order to make the lumber suitable for its ultimate use, it is then'necessary to redry this stock in kilns to an average of 5 to 10% moisture content. In my preliminary drying chamber, I accomplish a better equalization of moisture content of the various boards in a period of from 1 to 3 weeks, than that which might be accomplished in a yard in from 2 to 6 months. By the equalization of moisture content, in my preliminary drying chamber I eliminate two handlings of the stockthat is, one handling in the removal of stock to the yard and stacking it, and another in the unstacking and removal of it back for stacking on dry kiln trucks for kiln drying.

When the sapwood, which has a much higher moisture content than heartwood, is exposed to a drying atmosphere, it dries relatively faster than the heartwood. In my preliminary drying chamher I maintain a drying atmospheric condition which will preferably remove the moisture from the sapwood lumber as rapidly as it Uransfuses to the surface, thus permitting its moisture content to become equalized with the moisture content of heartwood. To accomplish this I employ the fan system illustrated, which circulates air preferably transversely across the stock loads, and which is preferably located along the floor line so as to exhaust the heaviest, most humid and most spent atmosphere from the preliminary drying chamber.

In drying substances, such, for example, as

lumber, I prefer to accumulate a kiln chargeof stock on suitable tracks in the preliminary drying chamber l0, preparatory to its being dried in the regular kilns 2. I therefore provide the housed preliminary storage chamber described above, in which stock loads may be stored and the difference in moisture content of the different pieces of lumber reduced during any desired period of time.

At times only part of the storage tracks may be filled with lumber. At other times all of the storage tracks may be filled. In any case I prefer to provide a circulating system which may be used at will for accomplishing a preliminary drying, preferably under controlled conditions employing a lower humidity and/or a higher temperature than outside atmospheric humidity and temperature while the stock is in storage.

My drying plant or combination dryer consists of a preliminary drying chamber III, a separate dry kiln 2 associated therewith, and a cooling and reconditioning shed 63' forming compartments preferably separated from each other, as illustrated in Figures VII and VIII. Each of the three compartments is preferably enclosed having side walls, roof, floor and doors, of reasonably tight construction. Each compartment may have separate and individual doors or use common doors or a common side wall with the adjacent compartment.

I preferably use a transfer car 12 at one end of the preliminary drying chamber I0, and at one end of the cooling shed 63, which permit putting a stock load on any of the tracks in the preliminary drying chamber In, or removing any of the stock loads from any of the tracks in the cooling shed 63.

The preliminary drying chamber is preferably located adjacent to the kilns 2, preferably in front of them, having tracks extending continuously through the kilns, but it may be located to one side of the kiln battery so that any of the stock loads on any of the several tracks 1!: the preliminary drying chamber may be transferred to any of the single track kilns 2 by the transfer car 12.

The operation of my preliminary drying chamber is substantially as follows:

Assuming that lumber has bmn stacked and placed on the storage tracks in the preliminary drying chamber, and the fans are rotated, the air will be circulated through the, stock loads illustrated in Figure III, for example, or recirculated through the stock loads, as illustrated in Figures IV and VI. It will be understood that part of the tracks may be empty, or they all may be filled. The heating pipes 20 and 2| when used, are preferably automatically controlled by means of the diaphragm valves 41, or or both, controlled by the thermostatic bulb 65, to maintain a definite temperature, and the steam spray supply pipes chambers respectively. The fans are rotated to circulate a controlled atmosphere through the stock loads, having preferably a predetermined temperature and humidity. The circulation of the atmosphere through the stock loads in the preliminary drying chamber may be continuous or intermittent as desired.

When regular kilns 2, of the charge or compartment type are used, the lumber on any one track, for example, may be removed from the preliminary drying chamber when desired, or when the equalization of the moisture content of the different boards has progressed to the desired point.

The lumber is then charged into a regular dry kiln 2, where a predetermined drying schedule is carried to dry it to the desired final average moisture content. After the stock has been dried in the regular kilns it is then conditioned in a cooling shed where it is allowed to cool pref-- erably below 140 F. and is preferably allowed to stand on kiln trucks to accomplish a substantial equalization of the moisture content distribution between the center and surface of each board. The period of time in the cooling shed to accom-.

plish this may vary from 12 to '72 hours. To help accomplish this I preferably maintain controlled conditions of heat and humidity in the cooling shed.

In some cases I prefer to accomplish the cooling and subsequent equalization of moisture content of each board in one of the regular dry kilns 2, after the drying process is complete. The kiln, equipped with humidity control, temperature control and means for circulation, is an ideal place to promote the equalization of moisture content in the individual boards.

When the kilns 2 cannot be spared for this purpost the cooling shed is preferably provided with heating, humidifying and circulation means and means for their control for this purpose.

Exhaust heated or humidified atmosphere from the kiln 2 may be used in the chambers Ill or 63 and vice versa to effect greater drying economy when desired.

fin important feature of my invention is the proce& which comprises preferably three steps, namely:

1. Preliminary drying of the stock for an indefinite period in accumulated storage under controlled conditions tending to equalize its initial moisture content. Initial moisture content is considered as the moisture content of the stock when the drying in the regular kilns is started.

2. Drying stock to the predetermined average moisture content in regular single track dry kilns 2 by removal of hygroscopic moisture. In some cases the moisture content is purposely made lower than that desired for ultimate use in order to permit absorption and better equalization later.

3. Substantial equalization of tension and compression stresses and moisture content distribution within each board, preferably under controlled conditions in a chamber prior tomanufacture. This latter step may promote the equalization of distribution moisture in each board without a substantial change in its moisture content. In some cases where t he stock has been kiln dried to a percent lower than that desired for its ultimate use, a controlled absorption of moisture is provided, by holding the stock at a temperature and humidity which will efiect the desired equilibrium moisture content which aids in the equalization aforesaid. For example holding the stock in the reconditioning treatment at a temperature of 178 and ahumidity of 72% will effect an equilibrium moisture content at 10%.

In the preliminary drying chamber, in the regular dry kiln and in the cooling shed or reconditioning chamber, I preferably employ, means providing air circulation transversely across boards in the stock loads.

It is understood that this invention is not limited to the exact design and form illustrated and described. Modifications of the structures and methods herein described are self-evident to those skilled in the art; therefore, it is to be understood that the invention includes within its scope 'whatever changes fairly come within either the terms or the spirit of the appended claims.

Having described my invention, what I claim is: 1. A drying plant comprising a preliminary drying chamber having enclosing walls, a dry kiln having an individual air circulating system for each track adjacent thereto, said preliminary drying chamber having a series of tracks therein and suitable for receiving stock loads of lumber, heating means in said chamber, a series of fans operatively mounted at track level adjacent to a side wall of said chamber, a fan duct extending substantially the full length of the chamber comprising a suction and an air delivery compartment on opposite sides of each of said fans, a fresh air supply and a ventilating port for each of said suction and air delivery compartments respectively on opposite sides of and in operative communication with a fan, controllable dampers in said ports, means for rotating said fan whereby air may be intaken through the port on one side of said fan and spent air exhausted from the air delivery compartment or recirculated transversely across stock loads on the series of tracks whereby effecting an equalization of the moisture content of the stock in said chamber, and means for removing stock loads from any o said tracks in said preliminary drying chamber and charging it into said kiln for individual treatment to dry the stock to the desired moisture content.

2. A drying plant comprising a preliminary drying chamber having inclosing walls and a series of tracks therein, means for controlling drying conditions of stock on said tracks therein, said means comprising heating pipes arranged between and adjacent to a pair of tracks, humidifying means therein, a series of fans at one side of said chamber operably mounted respectively between a series of inter-communicating compartments, each having a fresh air intake port or an outlet port therein and communicating with said chamber, a separate dry kiln adjacent thereto in which controlled drying conditions may be maintained, and a separate enclosed cooling shed adjacent to said kiln and having humidifying pipes therein, means of inter-communication for stock between the chamber, dry kiln and cooling shed aforesaid adjacent to said dry kiln, whereby boards to be dried are equalized in initial moisture content while in storage in the preliminary drying chamber, are dried by individual treatment to an average predetermined moisture content in the dry kiln, and are equalized in moisture distribution by high humidity treatment in the cooling shed.

3. A drying plant comprising a preliminary drying chamber, a dry kiln adjacent thereto havfans operatively mounted at intervals in said partition providing pressure and suction sides thereof in said kiln, a fresh air intake conduit extending substantially the full length of the kiln on each side of said partition, each of said conduits having controllable communication between one of its ends with said preliminary drying chamber, controllable communication of the opposite end of each of said conduits with the outside atmosphere, each of said conduits having ports at intervals along one of its sides in the kiln adjacent said fans.

4. A drying plant comprising a reconditioning chamber, a dry kiln adjacent thereto having heating means therein, a partition in said kiln, air circulating means comprising reversible rotary fans operatively mounted at intervals in said partition providing pressure and suction sides thereof in said kiln, a fresh air intake conduit extending substantially the full length of the kiln on each side of said partition, each of said conduits having controllable communication between one of its ends with said reconditioning chamber, controllable communication of the opposite end of each of said conduits with the outside atmosphere, each of said conduits effective to withdraw atmosphere from the conhaving ports at intervals in the kiln along one of its sides adjacent said fans.

In a drying apparatus, a kiln comprising an enclosure containing heating means, air circulation means and intake and outlet apparatus for controlling the state of the kiln atmosphere, a preliminary dryer adjacent the kiln that comprises an enclosure separated from the kiln, conduit means connecting said kiln with said preliminary dryer and air circulation means in said preliminary dryer that is efiective to draw heated atmosphere from the kiln through the preliminary dryer and discharge it external to both.

6. In a drying apparatus, a kiln, a, conditioning enclosure adjacent thereto but partitioned therefrom, conduit means through said partition between said kiln and said conditioning enclosure, a suction fan apparatus for said conditioning enclosure that is eflective to conduct atmosphere from said kiln into said conditioning enclosure and to discharge atmosphere from the bottom of the conditioning enclosure to the outside atmosphere.

7. In a drying apparatus, a kiln, a conditioning enclosure adjacent thereto but separated therefrom, conduit means positioned to conduct atmosphere from the kiln into the conditioning enclosure and a suction fan apparatus that is ditioning enclosure whereby to induce a flow of air from the kiln to the conditioning enclosure.

8. A drying plant comprising a preliminary drying chamber having enclosing walls, a dry kiln adjacent thereto and means for the transfer of stock therebetween said preliminary drying chamber having a series of tracks therein suitable for receiving stock loads of edge stacked lumber, a series of rotary fans mounted in a partition adjacent to a side wall of said chamber below said tracks, longitudinal openings between each of said tracks, intake compartments on one side of said partition having a passage connecting with said openings, said openings being graduated in size, the open area of the largest opening between the tracks being most remote from the said fan system and the open area of the smallest opening being closest to said fan system, means for rotating the fans whereby air circulation is produced transversely across the stock loads on the several tracks through said openings respectively and exhausted from said chamber by said fans, whereby efiecting an equalization of the moisture content of the stock preparatory to its being given individual treatment on a standard schedule in the single track dry kiln aforesaid.

JOSEPH I. STEEL. 

